A novel electromagnetic method is proposed for non-invasive measuring and reconstructing three-dimensional maps of the temperature distribution within the body or isolated tissues. This method is suggested as a means for determining the temperature in the general and immediate vicinity of in vivo tissues heated by microwaves, electrical currents or ultrasonic reduction for hyperthermia therapy of cancer. This method would have the advantage of providing absolute temperature tomograms which are nearly independent of tissue type. The method is based upon the use of an array of sensing electrodes placed on the surface of the skin surrounding the volume when the temperature distribution is to be determined. This scheme is predicted to ultimately reconstruct the three-dimensional temperature distribution within the body to about one or two centimeter spatial resolution by mathematical inversion of electrical noise data obtained from the array of electrodes. The detected electrical noise signal is generated within the body by temperature and electrical resistivity dependent microscopic current fluctuations. As a preliminary step, three-dimensional electrical conductivity maps are reconstructed from measurements of potential differences induced by active current injection. Temperature maps in three-dimensions are obtained by mathematical transformation of both the electrical conductivity maps and electrical noise data. The method will be verified by both computer simulation and experiment. Laboratory models will be constructed and tissue samples obtained and their internal temperature distribution will be determined by invasive but nonperturbing small fiber optic temperature probes, by ultrasound temperature tomography, and by the proposed electromagnetic method. The sensitivity and resolution and other characteristics of the electromagnetic method will be compared with those of the other two methods. The laboratory site has outstanding facilities and its staff is well prepared to conduct the proposed study.